Saturated fats may elevate circulating cholesterol by enhancing cholesterol absorption by the small intestine. This hypothesis will be investigated by studying jejunal cholesterol influx from mixed micellar solutions in conjugated bile salts which contain saturated fatty acids of different chain lengths and at low and medium levels of concentration. Jejunal cholesterol influx will also be compared for fatty acids of 18 carbon chain lengths which are saturated, monosaturated, polyunsaturated or artificially hydrogenated. The fatty acid will be used as such, or in the form of the monoglyceride ester, and in combinations of fatty acid and monoglyceride. In an attempt to delineate whether alterations in cholesterol transport are due to solution or tissue effects, the study will also include determination of cholesterol solubilization and partition between molecular and micellar phases as influenced by the composition and concentration of fatty acid included in the mixed micelle. These experiments will be performed in vitro. The data acquired from these absorption and solubilization experiments will be used to design further experiments in which solutions containing radiolabeled cholesterol will be fed to intact rats without or with antecedent dietary intake of selected fatty acids.